. The effects of inanition and malnutrition upon growth and structure . Entoderm^ ^Jf&^Eclbderro Fig. 8.—A longitudinal section of Hydra fusca after eight weeks of starvation. Body concontracted; mouth aperture still open. (After Berninger '10.) Fig. 9.—A longitudinal section of Hydra fusca after twelve weeks of starvation. Body oval in form; mouth aperture has closed. (After Berninger '10.) Hanel ('08) found that neither inanition nor low temperature causes sex- production in Hydra grisea. Krapfenbauer ('08) obtained positive results by lowered temperature, but not by inanition. Frischhol
. The effects of inanition and malnutrition upon growth and structure . Entoderm^ ^Jf&^Eclbderro Fig. 8.—A longitudinal section of Hydra fusca after eight weeks of starvation. Body concontracted; mouth aperture still open. (After Berninger '10.) Fig. 9.—A longitudinal section of Hydra fusca after twelve weeks of starvation. Body oval in form; mouth aperture has closed. (After Berninger '10.) Hanel ('08) found that neither inanition nor low temperature causes sex- production in Hydra grisea. Krapfenbauer ('08) obtained positive results by lowered temperature, but not by inanition. Frischholz ('09) found that within certain limits of temperature, sex-production in Hydra tends to appear in definite cycles of 20 to 40 days, depending upon the nutritional conditions. Even in extended inanition, however, sexual forms appear, either male or female (the strains used being always monosexual, never hermaphroditic). A change of temperature is unnecessary, but may accelerate sex-production. However, permanent exposure to high temperatures in Hydra grisea or to low tempera- tures in Hydra fusca, permanently inhibits sex-production, irrespective of the degree of nutrition. Finally, Berninger ('10) again found that in Hydra fusca (also in Dendrocoelum lacteum) inanition stimulates the development of the testes, with abundant ripening of the spermatozoa during starvation. In summary, it is evident that Hertwig was correct in concluding that sexual differentiation in Hydra is a complicated phenomenon, various factors being involved. Besides temperature and nutrition, there is probably a cyclic or seasonal variation, and other hereditary characteristics, apparently varying in different species or strains of Hydra.
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Keywords: ., bookcentury1900, bookdecade1920, bookpublis, booksubjectnutrition
